Magnetic freepoint indicator tool

ABSTRACT

A system for determining a stuck point of a pipe positioned within a wellbore includes a tubular housing and a sensor array positioned within the tubular housing. The system also includes ferromagnetic flux collectors and flux concentrators on either side of the sensor array. The flux collectors collect a magnetic flux that has been written to a portion of pipe. The flux concentrators intensify the flux to improve measurements of the flux that are acquired by the sensor array.

BACKGROUND OF THE DISCLOSURE 1. Field of the Disclosure

The present disclosure relates in general to downhole tools and moreparticularly to downhole tools utilized to assist with drillingoperations.

2. Brief Description of Related Art

During downhole drilling and recovery operations, portions of a drillstring may become stuck. For example, while wells are being drilledundesirable events, such as hole collapse, differential stick, keyseating, and the like may cause the drill string to become stuck withinthe formation. This situation is undesirable and may hinder drillingoperations. In addition, drill pipe may represent a significantinvestment, and as a result, recovering at least a portion of the drillpipe may be desirable. However, it is difficult to determine where thesticking point has occurred. As a result, operators either conductseveral runs to determine the sticking point, which is not costeffective, or leave large portions of the pipe in the formation.

SUMMARY OF THE DISCLOSURE

Applicants recognized the problems noted above herein and conceived anddeveloped embodiments of systems and methods, according to the presentdisclosure, for downhole identification.

In an embodiment, a method for determining a stuck point of a pipe isdescribed. The method includes writing a first magnetic profile along afirst portion of pipe and measuring a magnetic flux of the pipe. Themagnetic profile may be written to the pipe by applying a plurality ofmagnetic pulses to the pipe. A force is applied to the pipe and themagnetic flux is remeasured. Based on the difference between themeasured fluxes, the stuck point of the pipe may be determined. In someembodiments, if the change in flux does not meet a threshold, the fluxof a new portion of the pipe may be measured.

In another embodiment, a system is described that includes one or moremagnetic sources that pulse a magnetic field onto a pipe, and one ormore sensors to measure the magnetic flux. In some embodiments, thesystem may further include a drilling rig and a component to apply oneor more forces to a stuck pipe. The system includes the sensors andmagnetic source in a magnetic free point indicator tool, which may belowered into the pipe to determine where a stuck point exists.

In another embodiment, a system is described that includes a sensorarray arranged between two flux concentrators, which are situatedbetween two ferromagnetic flux collectors. The flux collectors collectthe magnetic flux that has been written to a pipe, and the fluxconcentrators intensify the flux to improve measurements of the fluxthat are taken by the sensor array. In some embodiments, the system ispart of an MFIT, which also includes one or more transmitters that writea magnetic profile to sections of the pipe. The flux collectors thencollect the flux and the sensor measures the flux. In some embodiments,the flux may be measured before and during a time when a force isapplied to the pipe. Based on changes in the flux, a stuck point of thepipe may be determined.

BRIEF DESCRIPTION OF THE DRAWINGS

The present technology will be better understood on reading thefollowing detailed description of non-limiting embodiments thereof, andon examining the accompanying drawings, in which:

FIG. 1 is a schematic side view of an embodiment of a drilling system,in accordance with embodiments of the present disclosure;

FIG. 2 is a schematic cross-sectional view of an embodiment of amagnetic freepoint indicator tool (MFIT), in accordance with embodimentsof the present disclosure;

FIG. 3 is a schematic view of the exterior of the tubular housing of anMFIT, in accordance with embodiments of the present disclosure;

FIG. 4 is a graph that illustrates the residual flux that is left on apipe after pulsing the pipe a plurality of times by a magnetic source;

FIG. 5 is a graph that illustrates residual flux that is measured withand without an embodiment described herein; and

FIG. 6 is a flow chart of an embodiment of a method for determining astuck point, in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The foregoing aspects, features and advantages of the present technologywill be further appreciated when considered with reference to thefollowing description of preferred embodiments and accompanyingdrawings, wherein like reference numerals represent like elements. Indescribing the preferred embodiments of the technology illustrated inthe appended drawings, specific terminology will be used for the sake ofclarity. The present technology, however, is not intended to be limitedto the specific terms used, and it is to be understood that eachspecific term includes equivalents that operate in a similar manner toaccomplish a similar purpose.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements. Anyexamples of operating parameters and/or environmental conditions are notexclusive of other parameters/conditions of the disclosed embodiments.Additionally, it should be understood that references to “oneembodiment”, “an embodiment”, “certain embodiments,” or “otherembodiments” of the present invention are not intended to be interpretedas excluding the existence of additional embodiments that alsoincorporate the recited features. Furthermore, reference to terms suchas “above,” “below,” “upper”, “lower”, “side”, “front,” “back,” or otherterms regarding orientation are made with reference to the illustratedembodiments and are not intended to be limiting or exclude otherorientations. Furthermore, like reference numbers may be used betweenfigures to illustrate like components, but it should be appreciated thatembodiments are not limited to utilizing like components.

Embodiments of the present disclosure include a magnetic freepointindicator tool (MFIT) that may be tripped into and out of a wellbore toidentify a stuck point of a pipe positioned within the wellbore. Invarious embodiments, the MFIT includes one or more magnetizing elements,such as a permanent magnet and/or a pulsed coil, to write a magneticflux onto the pipe (e.g., magnetize the pipe). Thereafter, one or moresensors may evaluate the magnetic flux of the pipe at a given location.The MFIT may then evaluate a change in magnetic flux, to a portion ofthe pipe, after a force is applied to the pipe. By the process ofmagnetorestriction, a force applied to a free portion of the pipe mayhave a changed magnetic flux, as compared to a fixed or stuck portion ofthe pipe. As a result, a comparison between the magnetic flux of thepipe before and after the force application may enable identification ofthe stuck point.

FIG. 1 is a schematic side view of an embodiment of a downhole drillingsystem 100 (e.g., drilling system) that includes a rig 102 and a drillstring 104 coupled to the rig 102. The drill string 104 includes a drillbit 106 at a distal end that may be rotated to engage a formation 108and form a wellbore 110. In various embodiments, the drill string 104 isformed from one or more tubulars that are mechanically coupled together(e.g., via threads, specialty couplings, or the like). As shown, thewellbore 110 includes a borehole sidewall 112 (e.g., sidewall) and anannulus 114 between the wellbore 110 and the drill string 104. Moreover,a bottom hole assembly (BHA) 116 is positioned at the bottom of thewellbore 110. The BHA 116 may include a drill collar 118, stabilizers120, or the like. It should be appreciated that the BHA 116 is providedfor illustrative purposes only and that various other components may becoupled to the drill string 104.

In operation, drilling mud or drilling fluid is pumped through the drillstring 104 and out of the drill bit 106. The drilling mud flows into theannulus 114 and removes cuttings from the face of the drill bit 106.Moreover, the drilling mud may cool the drill bit 106 during drillingoperations and further provide pressure stabilization in the wellbore110. In the illustrated embodiment, the drilling system 100 includesvarious tools 122, such as logging tools, which may be utilized toobtain measurements from the formation 108. These tools may be referredto as “logging while drilling” tools and may include nuclear tools,acoustic tools, seismic tools, magnetic tools, electrical tools, and thelike. Furthermore, while the illustrated embodiment includes the drillstring 104, it should be appreciated that various embodiments of thepresent disclosure may be incorporated into a wireline system, a coiledtubing system, or any other downhole investigation system.

FIG. 1 further illustrates a stuck point location 124. The stuck pointlocation 124 is a location where the drill string 104 and/or any otherpipe utilized in the system (e.g., production piping, casing, etc.) isstuck. Stuck refers to piping that cannot be withdrawn from the wellbore110 to the surface without intervention or significant forces. In otherwords, stuck piping may not be able to be tripped in/out of the wellborewithout intervention, such as applying additional force, which may beundesirable. Embodiments of the present disclosure may utilize a tool,such as a magnetic freepoint indicator tool (MFIT) to locate the stuckpoint location 124, based at least in part on an evaluation of magneticproperties in the pipe. For example, the MFIT may be utilized todetermine a stuck point within the wellbore, where one or morecomponents, such as drill pipe, has become lodged within the wellbore.

In some embodiments, a combination of an electromagnetic coil as well asa permanent magnet may be included. For example, the permanent magnetmay be positioned within the MFIT in one direction with theelectromagnetic coil positioned in the opposite direction. Thus,generated pulses may be maximized without saturating the magneticsignature.

In embodiments, the MFIT combines ferromagnetic collectors and fluxconcentrators to aid in identifying a stuck point. As a result, the MFITmay include one or more magnetic sources and one or more sensors tomeasure the residual pulse amplitude, among other measurements.Furthermore, additional components may also be utilized in combinationwith the MFIT. For example, in operation, an uphole component such as atable or top drive may be utilized in order to apply a force to thedrill pipe (e.g., a linear force, a rotational force, etc.). Thereafter,a change in the magnetic properties of a pipe region that experiencesstrain (the free end) may be measured, while regions that do notexperience strain (e.g., regions below the stuck point) will not have achange in magnetic properties. As a result, a measurement of a remnantmagnetic field, after magnetization of the pipe, may be utilized todetermine the stuck point. In this manner, the stuck region may beidentified and pipe upstream may be removed (e.g., unthreaded, cut,etc.) from the wellbore to enable operations to continue while savingthe pipe.

Traditional systems may include a tool consisting of a load cell and twoanchors or clamps, which are run into the pipe and anchored into place.Then the pipe is pulled or twisted. If the load cell measures a changein strain, the tool is located above the stuck point. If it measures nochange to strain, it is located below the stuck point. By continuingthis process along the length of pipe, the stuck point may eventually befound. However, this process is slow, which can be costly for producers.A variety of other tools may be utilized, each having various drawbacks.For example, pipe stretching evaluations are often inaccurate.Additionally, anchor tools are slow and do not lend themselves to acontinuous logging process. Sonic tools typically have signal/noiseproblems. Permeability measurements often have difficulties due tocurrents and low amplitudes.

Accordingly, embodiments of the present disclosure are directed toward amagnetic tool that determines the stuck point location 126 utilizingferromagnetic collectors (e.g., ferromagnetic cylinders, cylindricalrings) and flux concentrators. For example, in one embodiment, a sensoris arranged between two flux concentrators. Each of the fluxconcentrators intensify magnetic flux that is detected by one or moreferromagnetic collectors, such as ferromagnetic rings, that are arrangedat the opposite ends of the flux concentrators. Thus, changes in theaxial flux may be measured more accurately by the sensor, which measuresthe intensified flux.

In various embodiments, the MFIT is deployed when pipe is stuck, forexample during a drilling operation. In various embodiments, as notedabove, the MFIT includes two or more ferromagnetic flux collectors, fluxconcentrators, and at least one sensor between the inner ends of theflux collectors. On the down pass (e.g., tripping into the wellbore),the MFIT magnetizes the drill pipe. Sensors located above the magnetmeasure and/or log the baseline remote field from the flux generated inthe pipe. Next, the pipe is overpulled and/or torqued. For example, thedrilling rig may be used to apply a torsional or axial force to thepipe. The remote field from the remaining flux is logged again on the uppass (e.g., tripping out of the wellbore). As will be appreciated, thesensors may lead the magnet on the up pass. Comparisons of the logs showwhere stress has erased (e.g., reduced) the flux due to magnetostrictiveeffect.

Other embodiments of the present disclosure may enable an increase influx that may be applied to a pipe, thus allowing for improvedmeasurements of the flux profile that has been applied to the pipe. Onthe down pass of the MFIT, pulses from one or more electromagnets of theMFIT produce a flux signature or profile on the pipe. Further, magneticflux may be applied with one or more permanent magnets that apply themagnetic flux while passing along the pipe. By pulsing the magneticforce as opposed to just applying a single magnetic force, the fluxprofile of the pipe may be increased without causing other portions ofthe MFIT to become saturated with flux. On the up pass of the MFIT, theflux profile, now stronger than if the flux were applied by a singlemagnetic force, may be measured by one or more sensors of the MFIT. Witha combination of one or more permanent magnets and an electromagneticcoil, the pulse height may be maximized to improve resolution in readingthe flux difference.

FIG. 2 is a schematic cross-sectional view of an embodiment of an MFIT200 arranged in a pipe 300. The illustrated embodiment includes ahousing 202, which may be a tubular designed to withstand expectedwellbore pressures and temperatures. The housing 202 includes variouselectronics, which may include processors, memories, and communicationmodules to facilitate receipt and/or transmission of instructions and/ordata. For example, instructions may be received from a surface location,such as to begin pulsing the coil. Additionally, in embodiments,collected data may be transmitted to a surface location. However, itshould be appreciated that instructions and data may both be stored atonboard memory or memory that is coupled to the device for recordingpurposes.

Further illustrated is a primary sensor array 204 at a central locationof the tubular housing 202. The sensor array 204 may further includeassociated electronics. In various embodiments, the sensor array 204includes a plurality of sensors. Additionally, in one embodiment,additional radial sensor arrays 218 are arranged circumferentially aboutthe housing 202. As illustrated and further exemplified in FIG. 3, 8radial sensor arrays 218 are arranged on the housing 202 (an additional4 radial sensor arrays are positioned opposite the shown radial sensorarrays 218 which are present but not shown in FIG. 3). However, it iscontemplated that the additional sensors 218 may be arranged in otherconfigurations, including an MFIT with no additional sensors. By way ofexample only, the central sensor array 204 and/or additional radialsensor arrays 218 may include anisotropic magneto-resistive (AMR)sensors. However, it should be appreciated that a variety of differentmagnetometers with varying compositions and properties may be used withembodiments of the present disclosure, such as Hall effect sensors,magneto-diodes, magneto-transistors, GMR magnetometers, superconductingquantum interference devices (SQUIDs), flux-gates, sensing coils, or acombination thereof.

Additionally, transmitters 208 are arranged at ends of the MFIT 200, oneof which may be a downhole end of the tool (i.e., inserted into thewellbore first) and a uphole end of the tool. As noted above, theinitial run includes applying a baseline magnetic field to the pipe 300,which is collected by the ferromagnetic collectors 206 and intensifiedby the flux concentrators 210, and recording that field via the sensorarray 204. Then, as the tool is removed from the wellbore, the sensorarray 204 measures changes in the magnetic retentivity, also collectedby the ferromagnetic collectors 206 and intensified by the fluxconcentrators. In the illustrated embodiment, the sensor array 204 isoffset from the transmitter 208 by an offset distance 212, which may beparticularly selected based on a strength of the transmitter, a lengthof the tool, or the like. As will be appreciated, if the sensor array204 is too close to the transmitter 208, then the sensor array 204 maypick up magnetic data from the transmitter 208 and not the pipe 300.

When a drill pipe becomes stuck or otherwise immobile in the wellbore,the MFIT 200 may be tripped into the wellbore (e.g., lowered into thewellbore) in order to magnetize the pipe 300. In various embodiments,the transmitter 208 may include both a permanent magnet and/or anelectromagnetic coil 216 wrapped around a core. As the transmitter 208extends into the wellbore, the electromagnetic coil is activated, whichmay produce “bands” of magnetized material in the drill pipe 300 as wellas flux applied by a permanent magnet. In various embodiments, thesebands are produced approximately every 1 or 2 feet, and as a result, thetool may write hundreds or thousands of pulses within the wellbore. As aresult, there is both an axial flux and a radial flux. As a result, apatterned flux may be applied to the pipe 300, which may be detected bythe sensor array.

The pulsed magnetizing field may generate a flux connected in thin skin,close to the bore of the pipe 300. In some embodiments, anelectromagnetic coil may be pulsed a plurality of times to write a fluxpattern on the pipe 300. This may occur in conjunction with flux writtento the pipe by one or more permanent magnets. Without doing so, thewritten flux profile is more dilute, particularly with thick-walledcollars. As a result, the flux density when rapidly pulsing the magnetcoil multiple times may be much higher than from applying a single pulseat a location on the pipe 300.

FIG. 4 is a graph of residual magnetic flux after pulsing a pipe with aplurality of transmitter pulses. As illustrated, the graph includeslines representing a single pulse, two pulses, three pulses, and fourpulses. When a single pulse is written to a pipe, the residual magneticforce is approximately 750 units at a depth of 15. However, as morepulses are utilized in writing a magnetic signature to a pipe, theresidual flux increases, thus allowing for more accurate measurements ofthe flux when the profile is later checked. Thus, using the methoddescribed herein, applying a plurality of pulses improves the process ofdetermining a stuck point in a pipe.

FIG. 5 is a graph that illustrates measured residual flux in a pipe. Thegraph includes a baseline measurement (i.e., measurements with a“standard” MFIT that does not include embodiments described herein) andmeasurements taken by an MFIT that includes the flux concentrators asdescribed herein. As illustrated, the baseline measurement of flux at 15units is approximately 3,000. However, by implementing the MFIT withferromagnetic collectors, flux concentrators, and a central sensorarray, the same measurement position results in approximately 8,000units of flux. Thus, because the measured flux is substantially higherwhen the concentrator configuration is utilized, greater accuracy andimproved resolution of measurements can be achieved using the same typeof sensor array.

FIG. 6 is a flow chart of an embodiment of a method 600 for determininga stuck point in a wellbore, for example a stuck point of pipepositioned within the wellbore. It should be appreciated that for thismethod, and other methods described herein, that the claims may beperformed in a different order, or in parallel, unless otherwiseexplicitly stated. Moreover, there may be more or fewer steps andcertain steps of the method may be optional. During a drillingoperation, a pipe may become stuck in a wellbore, as noted above. It maybe desirable to retrieve at least a portion of the piping downhole, asthe pipe may be costly for operators. During recovery operations, thepipe may be cut or unthreaded at a location uphole of a stuck point,thereby allowing the unstuck portions to be freely removed. However, itmay be difficult to identify the stuck point. Embodiments of the presentdisclosure may utilize the MFIT to position a tool within the pipe toidentify the stuck point. The tool may be run into the pipe (e.g.,lowered downhole into the pipe) to write a magnetic profile on the pipe904. The magnetic profile may be from an electromagnet that isincorporated into the MFIT. In various embodiments, the magnetic profilemay be written to the pipe by pulsing the electromagnet a plurality oftimes to increase the intensity of the resulting profile.

In various embodiments, data is acquired that corresponds to a firstmagnetic flux of the pipe 906. The first magnetic flux may be associatedwith the magnetic flux generated by the magnetic profile. As described,data may be acquired via downhole sensors incorporated into the MFIT. Invarious embodiments, the data acquisition includes a profile thatillustrates the first magnetic flux as a function of a location along anaxial length of the pipe. That is, one or more position sensors may beincorporated in order to determine a location of different magnetic fluxmeasurements. In some embodiments, the acquired data may be measured bya sensor array and a configuration with flux concentrators, as describedherein.

As noted above, magneto-restriction may enable the MFIT to identify thestuck point by comparing how magnetic flux changes in areas of the pipein response to an applied force. In some embodiments, the magnetic fluxmay be measured while the force is applied to the pipe. Alternatively,the magnetic force may be measure after the force has been applied tothe pipe. Accordingly, the method may also include applying a force tothe pipe 908 and alternatively, apply and ceasing applying force to thepipe. This force may be an axial force (e.g., a pull or push), a radialforce, a torsional force (e.g., a twist), or a combination thereof.Next, a second data acquisition process may correspond to a secondmagnetic flux in the pipe 910. The second magnetic flux may correspondto a change resulting from the applied force. In other words, the secondmagnetic flux may be referred to as the magnetic flux measured after theapplication of the force. For example, as noted above, the area of thepipe above the stuck point is anticipated as having a reduced magneticflux due to magnetostriction while the area blow the stuck point isanticipated as having the same or substantially same magnetic flux. Thesecond data acquisition event includes tripping the MFIT out of thepipe/wellbore such that the sensor array is first, with respect to themagnetic sources. As a result, the permanent magnetic will notre-magnetize or modify the readings, and moreover, the pulsed coil maybe shut off during the second data acquisition event. The second dataacquisition event, like the first data acquisition event, may alsocorrelate the magnetic flux to the wellbore position, thereby enablingcomparison with the first magnetic flux.

In various embodiments, the first and second magnetic fluxes arecompared at a corresponding location 912. For example, each magneticflux may be evaluated at an equal or substantially equal location withinthe pipe. The comparison may evaluate a difference or change in themagnetic flux, for example, against a threshold 914. If the differenceexceeds the threshold, the stuck point may be determined 916. However,if the difference does not exceed the threshold, additional data may beconsidered 918. If there is additional data 920, those correspondingpoints may be reevaluated against the threshold. If there is noadditional data, the method may end 922. In this manner, variouspositions along a length of the pipe may be evaluated to determine thestuck point.

Although the technology herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent technology. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present technology as defined by the appended claims.

What is claimed is:
 1. A method for identifying a stuck point of a pipearranged in a wellbore, comprising: writing a first magnetic profilealong a first portion of the pipe by pulsing a first magnetic force aplurality of times; acquiring a first magnetic flux over the firstportion of the pipe; applying a force to the pipe; acquiring a secondmagnetic flux over the first portion of the pipe once the force has beenapplied and removed; and determining a first flux difference, whereinthe first flux difference is a difference between the first magneticflux of the first portion of the pipe and the second magnetic flux ofthe first portion of the pipe.
 2. The method of claim 1, furthercomprising: writing a second magnetic profile along a second portion ofthe pipe by pulsing a second magnetic force a plurality of times;acquiring a first magnetic flux over the second portion of the pipe;applying a second force to the pipe; acquiring a second magnetic fluxover the second portion of the pipe once the force has been applied andremoved; and determining a second flux difference, wherein the secondflux difference is a difference between the first magnetic flux over thesecond portion of the pipe and a second magnetic flux over the secondportion of the pipe.
 3. The method of claim 2, further comprising:determining that the pipe is stuck between the first portion of the pipeand the second portion of the pipe based on the first flux differenceand the second flux difference.
 4. The method of claim 3, wherein: thefirst flux difference does not exceed a threshold; and wherein thesecond flux difference exceeds a threshold.
 5. The method of claim 2,wherein the first magnetic profile and the second magnetic profile arewritten by an electromagnetic source.
 6. The method of claim 2, furthercomprising: determining that the pipe is not stuck between the firstportion of the pipe and the second portion of the pipe based on thefirst flux difference and the second flux difference.
 7. The method ofclaim 6, wherein; the first flux difference does not exceed a threshold;and the second flux difference does not exceed a threshold.
 8. Themethod of claim 6, further comprising: Writing a third magnetic profilealong a third portion of the pipe, wherein the third portion is moredown the pipe than the first portion and the second portion.
 9. Themethod of claim 1, wherein the plurality of pulses is three pulses. 10.The method of claim 1, wherein the magnetic force is applied by amagnetic source comprising an electromagnet.
 11. The system of claim 1,wherein the sensors include at least one of anisotropicmagneto-resistive sensors, Hall effect sensors, magneto-diodes,magneto-transistors, GMR magnetometers, superconducting quantuminterference devices (SQUIDs), flux-gates, sensing coils, or acombination thereof.
 12. A system for determining a stuck point of apipe positioned within a wellbore, comprising: a tubular housing; amagnetic source positioned within the tubular housing; and a controller,wherein the controller causes the magnetic source to pulse a pluralityof times to write a first magnetic profile along a portion of the pipe;and a sensor array positioned within the tubular housing, wherein thesensor array measures a first magnetic flux over the first portion ofthe pipe.
 13. The system of claim 12, further comprising: a forcegenerator, wherein the force generator applies a force to the pipe;wherein the sensor array measures a second magnetic flux over the firstportion of the pipe after the force generator applies the force to thepipe.
 14. The system of claim 12, wherein the sensor includes at leastone of anisotropic magneto-resistive sensors, Hall effect sensors,magneto-diodes, magneto-transistors, GMR magnetometers, superconductingquantum interference devices (SQUIDs), flux-gates, sensing coils, or acombination thereof.
 15. A system, comprising: a drilling rig, thedrilling rig installing one or more sections of pipe into a wellboreformed in a downhole formation; a stuck section of pipe, of the one ormore sections of pipe, the stuck section of pipe being positioned in thewellbore and having a free end, a stuck end, and a stuck point betweenthe free end and the stuck end; and a magnetic freepoint indicator tool(MFIT), comprising: a magnetic source configured to pulse a plurality oftimes to write a first magnetic signature along a first portion of thepipe; and a sensor array configured to measure a magnetic flux over aportion of the pipe.
 16. The system of claim 15, wherein a magneticsaturation of one or more portions of the MFIT does not exceed athreshold while writing the magnetic profile.
 17. The system of claim15, wherein the magnetic source is an electromagnet.
 18. The system ofclaim 15, wherein the sensor array measures a first magnetic flux when aforce is not applied to the pipe, and wherein the sensor array measuresa second magnetic flux when the force is applied to the pipe.
 19. Thesystem of claim 18, wherein a difference between the first magnetic fluxand the second magnetic flux exceeding a threshold is indicative of theportion of the pipe being closer to the free end than the stuck end. 20.The system of claim 15, wherein the MFIT includes a plurality of sensorarrays.